Recently, in order to improve the image quality of a camera (imaging device) built in a portable electronic apparatus, the number of pixels in an imaging element mounted on the camera is increasing. An imaging device built in a portable electronic apparatus in some cases has an autofocus function to improve the quality of captured images. Autofocusing is performed by an electric actuator moving an optical system in an imaging device in an optical axis direction by electricity.
Conventional electric actuator mechanisms are, for example, such that a magnet is arranged around a holder that holds a plurality of lenses and a support that holds the holder includes a coil. Moreover, the holder is connected by a spring. The balance between the Lorentz force acting between the coil and the magnet and the elastic force of the spring is adjusted by causing current to flow in the coil. Consequently, the position of the holder in the optical axis direction is controlled, thereby realizing an electric actuator.
In an imaging device, the pixel spacing is reduced with an increase in pixel density of an imaging element, therefore, the resolution required of a lens is increasing. Thus, the number of lenses is increased to four or more from three in conventional imaging devices. If the number of lenses increases, the weight of the holder including the lenses increases, therefore, the coil and the magnet for an electric actuator increase in size and thickness, which results in increasing power consumption.
However, in order to reduce the size and the thickness of a portable electronic apparatus, a demand for reducing the size and the thickness of an imaging device is growing. Therefore, it is desirable to reduce the size and the thickness of an electric actuator for autofocusing.